Electrically controlled valve means



June 14, 194. E. A. ROCKWELL.

ELECTRICALLY CONTROLLED VALVE MEANS Filed. May 24, 1945 Pressure a2 .50 ur ce Patented June l4, 1949 ELECTRICALLY CONTROLLED VALVE MEANS Edward A. Rockwell, Cleveland, Ohio, assignor, by

mesne assignments, to Borg-Warner Corporation, Chicago, 11]., a corporation oi Illinois Application May 24, 1945, Serial No. 595,578

14 Claims. (Cl. 12141) 1 My invention relates particularly to an app ratus for controlling the movement oi any device for performing work by means of an electric control connection which operates the device hydraulically, and while my invention is applicable to the control of devices of any desired character, it is particularly applicable to the controls in the operation of aircraft.

The object of my invention is to provide an electric-hydraulic control apparatus, by means of which any device to be moved may be operated thereby and in which an electric control device vide an arrangement of this character which,

while the device that is to be controlled may be located at a considerable distance from the electric controlling mechanism for the same, substantially the same effective control is obtained as if the parts were entirely hydraulic and located in proximity to one another. A further object is to-provide an apparatus of this character in which the delivery pressures are eflectively co-related to the manual forces applied for operating the electric control apparatus therein. Another object is to provide, in an apparatus of this character, an electrical valve operating mechanism having a progressively decreasing leverage to compensate for changes inposition of the electrical actuating means therefor. Still another object is to provide a manual control means which is coordinately pressdre-responsive to the hydraulic pressures delivered thereby. A further object is to provide a compact, selfcontained, powerful, eficient and light weight power unit which can be placed wherever desired with simple tubing and electrical connections. A further important object is to provide the same for effectively operating airplane wheel brakes. Another'object is to provide a quick-acting release control mechanism. A further object is to translate manual pressures from the pilot and co-pilot to the servomotor by a single line to the brakes. Still another object is to conserve the amount of high pressure fluid utilized to operate the control apparatus by means of modulator valves. Accordingly, a relatively small lightweight apparatus can be used for this purpose. Furth'er objects of my invention will appear fromthe detailed description of the same hereinafter. 1

While my invention is capable of embodiment in many diiierent forms. by way of illustration I have shown only certain forms thereof in the accompanying drawing, in which- Fig. 1 is a diagrammatic elevation, partly in section, of an apparatus constructed in accordance with my invention; and

Fig. 2 is a diagrammatic vertical section of a modified form of the valve actuating mechanism therein.

In the drawing, referring first to the form of my invention as shown in Fig. 1, I have shown a pedal l for operation by the pilot of an airplane, the same being mounted on a pivoted shaft 2 carried in the end of a rudder lever 3, which is fastened to a shaft 4 having a stationary pivot on the airplane. To this shaft 5 there is attached an arm 5 which is connected by a link socket 6 to the rubber or rudders of the airplane (not shown). Secured to the pedal l, furthermore, there is an arm I having a pivotal connec tion 8 to a link 9 which is connected to an arm secured on a shaft ll carried in fixed pivots by the airplane. Also secured to the shaft ii there is an arm H which operates on a curved outer surface it of a lever it having a pivotal supp rt 5 in brackets it secured to a spring housing ll having provided therein a reaction means in the form of a helical spring 58, one end of which is seated on the spring housing ll and the other end of which presses against a flange member is which is secured on a plunger rod 20 having a pivotal connection 2! to the middle portion of the lever it. The other end of the plunger rod 26 extends out through the end of the spring housing l9 and is provided with a. sleeve 22 having a switch arm 23 thereon. The arm 23 is provided with a contact 26 so as to make contact in succession with a series of terminals 25 connected to a rheostat resistance .25.

A co-pilot pedal 2'8 is provided in the same airplane with connecting parts the same as just described, as being provided for the pilot and connected to the pedal i, so that thereby the co-pilot may operate rheostat connections 28 and 29 connected to a rheostat resistance 36 in in the same manner as previously described in connection ,with the pilot pedal l. The sleeve 22 is connected by a wire 3! to a wire 32 leading from the co-pilot rheostat terminal 28 and these two wires are, accordingly, both connected by a wire 33 to one terminal of a storage battery 33, the other terminal of which leads by a wire 31 to branch wires 38 and 39 connected, respectively, to electromagnets 40 and M which are located on opposite sides of an armature switch arm 42 arranged to be magnetically attracted by either to the field winding of a valve-operating solenoid 44 within a casing 45. Furthermore, the electromagnet 48 is connected by a wire 46 to a wire 41 having a branch 48 leading to a terminal 48a,

the circuit through which can be completed by the movement of the arm 42, and the wire 41 thence leads to a contact 48 which is connected to a spring arm terminal 49 which is capable of being moved by the armature 42 so as to break the circuit between the contact 48 and the spring arm 49, the latter being connected by a wire 58 to one end of the rheostat resistance 28. Similarly, the electromagnet 4| is connected by a wire to a wire 52 which has a branch 58 leading to a contact 54 which is provided for completing a circuit through the armature 42 when moved by the electromagnet 4|. The said wire 52, in a similar manner, leads to a contact 55 which completes the circuit with a spring arm 58 so that the circuit between the same and the contact 55 can be broken by pressure from the end of the armature 42 when moved by the electric magnet 48. This spring contact 58 is, furthermore, connected by a wire 51 to one'end of the rheostat resistance 88.

The wires 88 and 89 leading to the electromagnets 48, 4| are also connected by a wire 58 to the solenoid 44. Within the casing 45 of the solenoid 44 there is a centering screw 59 having a lock nut 88 thereon, the said screw being provided with a conical end 8| for acting as a centering means within a conical recess 82 in an iron core 83 of the solenoid 44. The core 88 is provided with a yoke 84 on a reduced extension 85 passing through an opening 65 which leads to the chamber in which the solenoid 44 is carried. The yoke 64 is attached at its lower side by a pivot 51 to a rocker arm 58 carried on a pivot 89 in the sides of the casing 45, within a chamber 18 be neath the opening 55. It will be noted that the lower face of the lever arm 88 has a curved surface 1|, the curvature of which is selected to accord with the characteristics of the windings of the solenoid, for contacting with the outer end of an arm 12 carried on a fixed pivot 13 in the casing 45 within the said chamber 18. This casing 45 is secured in any desired manner to the top' of an intermediate casing 14 which has a chamber 15 therein connected by a port 18 to the chamber 18. Furthermore, the said arm 12 is supported upon the rounded upper end of a plunger rod 11 which passes through the top of the intermediate casing 14 into the chamber 15. Also, thelower end of the plunger rod "has a rounded end contacting with the upper surface of a rocker plate 18 having two hemispherical recesses 19 and 88 for-receiving in the under face of said plate 18 an inlet valve rod 8| and an outlet valve rod 82. The valve rod 82 has a helical retracting spring around the same, thelower end of which is received in a recess 84 in the top of a valve casing 85, the upper end of the spring 88 being located against a-spring retaining ring 85 in the chamber 15 fastened to the rod 82. The valve casing 85, which may be secured to the intermediate casing 14 in any desired manner, is

provided with vertical passages 81 and 88 to re-' ceive the rods 8| and 82, respectively. At the top of the passage 81 there is a screw-threaded rece 81a to receive a. screw plug 811) which exerts a predetermined pinch on the rod 8| by a compres- 4 sible gasket 81c between washers 81d, of substantially rectangular cross-section, and 81e located above a dished washer 81!. By this means the normal friction is minimized and the friction exerted on the plunger 11 will be the same when increasing forces as well as decreasing forces are applied to the rod 8|. The rod 8| extends downwardly through an inlet chamber 89 for receiving a high pressure liquid from any desired source through a screw-threaded inlet opening 98 which has any desired tubular connection for this purpose. Within the chamber 89 the rod 9| has a reduced end 9| carrying a conical valve 92 thereon which is arranged to seat against a removable annular valve seat 93 supported by a shoulder 94 adjacent to the chamber 89. Furthermore, beneath the valve 92 the rod 8| has a boss 95 to act as a guide for the helical spring 95, the upper end of which rests against the conical valve 92 while the lower end is supported in a recess 91 in a cover plate 98 provided with a-chamber 99 therein and having a screw-threaded outlet port I88 which may be connected by any suitable tubular means I8I to a passageway I82 in a casing I83 of a work-performing piston I84 on a piston rod I85 normally moved to the right, in Fig. 1, by a helical spring I86 against a movable disc I81 held in place by a supply ring I88 located in a recess I89. Furthermore, the chamber 99 has a discharge port 8 within a valve seat ring III supported against a shoulder H2 in the valve casing 85 adjacent to a chamber H3 which receives the lower end of the outlet valve rod 82 where said rod is provided with a conical valve 4 to cooperate with a valve seat I I5 on the upper portion of the valve seat ring H I. Also, the chamber H8 is connected with an outlet or discharge port II8 which is screw-threaded to receive any desired tubular connection for receiving the liquid when being discharged. It will be understood that the piston I83 may be a valve operating piston, as for instance the valve operating piston such as is shown in Fig. 2 of my co-pending application Ser. No. 534,503, filed May 6, 1944, upon Electrical hydraulic power unit, Patent No. 2,443,642.

As shown in Fig. 2, I may provide a modification of the valve actuating mechanism in which it will be noted thatthe valve casing 85 is provided with the inlet valve rod 8| and outlet valve rodi82 as previously described. Also, these rods 8| and 82 are operated by the same kind of rocker plate 18 as in the preceding form in Fig. 1, as well as the spring 88 shown therein. However, in this instance the upper ends of the rods 8|- and 82 are received in a chamber 1 in a solenoid casing I I8, having a chamber I I9 therein and a passageway I28 which receives a valve operating plunger |2| resting on the upper face of the rocker plate 18. In this instance, furthermore, the upper end of the plunger "I is connected by a pivot I22 to a link I29, the other end of which is provided with a pivotal connection I24 to a pair of toggle levers I25 and I25.

The toggle lever I25 is provided with an adjusting rod I21 having a slot I28 cooperating with a stop pin I29 passing through an extension I88 of the solenoid casing H8. The outer end of the rod I21 has secured thereto a screw |3I around the outside of which there is an adjusting sleeve nut I32 provided with a. flange I88 resting against the outside end of the extension .l38. A look nut I34 has an annular shoulder I fitting against the outside of the flange I38 for securing the same in adjusted position. Within the chamber II9, furthermore,

there is a'solenoid field coil nected by the wires 43 and 58 to the other parts of the control mechanism, as in Fig. 1. The field coil I36 has within the same an iron core I31 which carries a pivot I38v for connection to the toggle levers I25 and I26. The other end of the core I31 is also provided with a conical recess I39 for cooperating with a conical end I40 of a guiding screw I4I having a lock nut I42 and which is screw-threaded in the solenoid casing I18.

In the operation of my invention, referring first to Fig. 1, the pilot may operate the pedal I or the co-pilot may operate the pedal I21 for controlling the movement of the work-performing piston I04, the latter being provided for operating any of the desired parts of the aircraft to be con-.

I and 21 operatesin the same manner and theoperation of only one thereof will be described in detail accordingly. When operating the pedal I it will be understood, of course, that by means 1 I36 which is confrom the pivot 69 or axis of rotation of the lever arm 68 and thereby shift the point of applica- -tion of force between the lever arms 68 and 12 the plunger 11, being nearer to the outlet valve V of the arm 5 the rudderof the aircraft may be" controlled by moving the rudder lever 3 about.

this fixed pivot 4. As this occurs, however, it

link 9 will be mounted in parallel to each other.

In this way, by the rotation of the pedal I around .25 will be noted that the rudder lever 3 and the rod 82, theoutlet valve H4, H5 is closed, after which the valve 92, 93 is opened to the desired extent, thus admitting high pressure liquid from the inlet port 90 which enters the chamber 99 and thence passes downwardly by the pipe IOI to move the piston I04 against the force of the spring I06, to actas'a servomotor. As fluid pressure builds up in the chamber 99 and port H0 and exceeds the mechanical force or pressure applied by the energizedwsolenoid core 63 to the discharge valve rod 82 and with which force the rod 82 is thrust down, the fluid pressure reacts to move the valve rod 82 upward to open the discharge passage IIO to permit the pressure fluid of the inlet valve rod 8I as afu'lcrum to thererotate the lever 12 upwardly about its pivot 13.,

successive advance of the contact 24 over the] contacts 25 the resistance of the rheostat will be successively decreased so as to increasingly energize the solenoid 44. The closing of the rheostat connections 24 and 25 willenergize the electromagnet through the wires 33, 3|, contacts 24, 25, wire 80, contacts 49, 48, wires 41; 46, magnet 40 and wires 38 and 31, thus attracting the armature 42 and completing the circuit between the armature 42 and the terminal 49 to energize the solenoid 44 while at the same time pushing the spring 56 away from the con-- I tact and thus preventing the control of the apparatus being altered by the operation of the copilot pedal 21 during the operation from the pedal I. The circuit through the solenoid is completed through the wires 33 and 3|, contacts 24, 25, wire 50, contacts 49, 48, wire 41, terminal 48a, armature 42, wire 43, wire 58 and wire 31. The same will take place in the reverse order, when the co-pilot pedal 21 is operated by energizing the magnet 4 I' instead of the pilot pedal I. Thus, in the operation of the pedal I as the contact by cause the plunger 11 to move upwardly and Due to the engagement of the lever 12 with the cam surface 1| of the lever 68, the lever 68 will be rotated in a clockwise direction about its fixed pivot 69 and, through-its pivotal connection at 61 to the solenoid core 63, will exert a downward pull on the core 63 in opposition to the upward pull on the core exerted by the field coil of the solenoid 44. According to the extent of the movement of the piston. I04 a corresponding reaction is produced on the pedal I due to the increasing opposition of the spring I8 to the further movement of the pedal I. When the manual pressure on the pedal I M21 is being relaxed the same corresponding reaction or "feel" will begization of the solenoid 44 whereby the core 63 24 is advanced over the series of contacts 25 an 1 increased energizing of the solenoid 44 takes place, thus moving to the desired extent the cam surface H of the lever 68 downwardly againstthe lever arm 12. It may be noted that the cam surface H on the bottom of the lever arm 68 is arcuately convexly formed and constitutes a curve from one end of the arm to the other, the curve gradually extending upwardly from the portion thereof beneath the pivot 69 to the left extrem ity of the arm 68. Upon increasingly energizing the solenoid 44 and a consequent movement of the core 63 in an upward direction, the movable pivot 61, connecting the arm 68 and core 68, is also movedupwardly and the arm 68 is rotated in a counterclockwisedirection about its fixed pivot '69 whereby rotation'ofthe curved surface II of the arm 68 will cause the lever arm 12 to engage the surface ata varyingdistance thereof is operative to control themodula-ting valve to permit increasing fluid pressure on the piston I04. While the pressure is being relaxed from the pedal I or the pedal 21 the pressure liquid will be allowed to discharge past the valve H4, H5 to the discharge port H6. At any point where the pedal is stopped, however, the valves 92, 93 and H3, H4 will be in lap position.- This action will continue to the extent desired orun til all of the high pressure liquid-has been released from the pipe IOI to be discharged through the discharge port H6 and until the partshave thus been restored to their initial positions.

In the modified form of my invention as shown in Fig. 2, theoperation is the same as that already described except that in this instance the decreasing mechanical advantage is secured by the toggle levers I25, I26 in connection with the link I23 and the plunger I2I. Also, in this instance it will be noted that the extentof this decreasing mechanical advantage can be adjusted or'set to any desired proportion by means of the sleeve nut I32 which, when adjusted, is maintained in its adjusted position by the lock nut I34. More particularly, the adjustment for securing the decreasing mechanical advantage of V the toggle lever connection to the plunger I2I may be readily obtained by rotating the lock nut I34 to free the same from the flange I33 of the sleeve nut I32 to permit rotation of the nut I32 which will, due to its threaded engagement I3I secured to the rod I21, cause movement of the rod I2I to the left thereby moving the levers I25 and I26 and the core I39 in the same direction. Due to these movements afforded by the pivotal connections of the lever I25 with the rod I21, the lever I26 to the core I39, and the connection of the levers at the pivot I24, the levers and core will be shifted to the left and with them the upper portion of the link I23 connected thereto eifecting an inclination of the link to the left, due to its pivotal connection I22 to the plunger I2I which is maintained in its vertical position between the walls of the opening I20. Upon energization of the solenoid I I8 and movement of the core I39 to the right the angle of inclination of the link I23 will be such as to dispose the angular inclination of the levers I25 and I26 in almost coplanar relationship which will result in decreasing the mechanical advantage of the levers I25 and I2-6 in connection with the link.l23 and plunger I2I. Upon energization of the solenoid and movement of the core I39 to the right, the approach of the pivot I24 and the levers to a common horizontal plane by the aforesaid adjustment will decrease the amount of travel of V the levers toward said plane and thereby the travel of the link I23 and plunger I2I effecting operation of the rocker plate I8 and thereby the valve rods BI and 82.

By this means, therefore, modulating valve control of the movement of the work-performing device may be readily secured with substantially the same effectiveness of control as if the apparatus were entirely hydraulic, but in this instance any desired remote position can be provided for the manual controls without thereby in any way altering the speed or effectiveness of the work-performing hydraulic fluid. This is accomplished, also, by securing a degree of travel of the solenoid in each of the forms of my invention described which is coordinate to the extent to which the control mechanism has been operated and according to the hydraulic pressure delivered for the operation of the workperfcrming device.

While Ihave described my invention above in detail I wish it to be understood that many changes may be made therein without departing from the spirit of the same.

I claim:

1. In combination, a source of fluid pressure, a modulating valve controlling the delivery of increasing pressures to a device to perform work,

and an electrical control mechanism remote from said modulating valve and connected thereto by an electric circuit having a valve-operating solenoid therein provided with a lever connection to said valve arranged to control the operation of said valve and affording a decreasing mechanical advantage between said valve and solenoid, said control mechanism having a manually operated reaction device in said circuit for effecting energization of said solenoid and adapted to produce a reaction corresponding to c the pressures delivered.

2. In combination, a source of fluid pressure, a modulating valve controlling the delivery of increasing pressures to a. device to perform work, and an electrical control mechanism remote from said modulating valve and connected thereto by an electric circuit having a valve-operating solenoid therein provided with a lever connection to said valve arranged to control the operation of said valve, said lever connection having a cam affording a decreasing mechanical advantage between said valve and solenoid, said control mechanism having a'manually operated reaction device in said circuit for effecting energize,- tion of said solenoid and adapted to produce a reaction corresponding to the pressures delivered.

3. In combination, a source of fluid pressure, a modulating valve controlling the delivery of increasing pressures to a device to perform work, and an electrical control mechanism remote from said modulating valve and connected thereto by an electric circuit having a valve-operating solenoid therein provided with a toggle leverlconnection to said valve arranged to control the operation of said valve and affording a decreasing mechanical advantage between said valve and solenoid, said control mechanism having a manually operated reaction device in said circuit for effecting energization of said solenoid and adapted to produce a reaction corresponding to the pressures delivered.

4. In combination, a source of fluid pressure, a modulating valve controlling the delivery of increasing pressures to a device to perform work, and an electrical control mechanism, having alternately operable dual controls therein, remote from the modulating valve and connected thereto by an electric circuit having a valveoperating solenoid therein, arranged to control the operation of the said valve, said control mechanism having an electro magnet arranged to close the circuit with the solenoid when one of the controls is operated and a circuit connection operated by the magnet to disconnect the other control from operating the solenoid, said control mechanism havingmanually operated reaction devices associated with respective controls and selectively operable thereby to energize 'said electro magnet and adapted to produce a reaction corresponding to the pressures delivered.

5. In combination, a source of fluid pressure, a modulating valve controlling the delivery of increasing pressures to a device to perform work, and an electrical control mechanism, having alternately operable dual controls therein, remote from the modulating valve and connected thereto by an electric circuit having a, valveoperating solenoid therein, arranged to control the operation of the said valve, each of said controls having a reaction device operatively connected to said control mechanism to effect energization of said solenoid producing a mechanical reaction corresponding to the pressures delivered, said control mechanism having a pair of electro magnets and a pair of switches having a switch arm forming the armature of the electro magnets, arranged to close the circuit with the solenoid when one of the reaction devices is operated and a circuit connection operated by the magnets to disconnect the other reaction device from operating the solenoid.

6. In combination, a source of fluid pressure, a modulating valve controlling the delivery of increasing pressures to a device to perform work, and an electrical control mechanism having alternately operable dual controls therein, remote from the modulating valve and connected thereto by an electric circuit having a valve-operating 9 solenoid therein, arranged to control the operation of the said valve, each of said controls havsorted in said circuit to effect energization of ing a reaction device operatively connected to disconnect the other reaction devices from operating the solenoid.

7. In combination, a source of fluid pressure, a modulating valve controlling the delivery of increasing pressures to a device to perform work, and an electrical control mechanism, having alternately operable dual controls therein, remote from the modulating valve and connected thereto by an electric circuit having a valve-operating solenoid therein, arranged to control the operation of the said valve, each ofsaid controls having a reaction device operatively connected to said control-mechanism to effect energization of said solenoid and producing a mechanical reaction corresponding to the pressures delivered, said solenoid having a leverage connection to the valve, said connection having a cam providing a decreasing mechanical advantage upon energization of said solenoid, said control mechanism having a pair of electromagnets and a pair of switches having a switch arm forming the arma-' ture of the electr c-magnets, arranged to close the circuit with the solenoid when one of the reaction devices is operated and a. circuit connection operated by the magnets to disconnect the other reaction device from operating the solenoid.

8. In combination, a source of fluid pressure, a modulating valve controlling the delivery of increasing pressures to a device to perform work, and an electrical control mechanism, having alternately operable dual controls therein, remote from the modulating valve and connected thereto by an electric circuithaving a valve-operating solenoid therein, arranged to control the operation of the said valve, each of said controls having a reaction device operatively connected to said control mechanism to efiect energization of said solenoid and producing a mechanical reaction corresponding to the pressures delivered, said solenoid having a toggle leverage connection to the valve, providing a decreasing mechanical advantage upon energization of said solenoid, said control mechanism having a pair of electromagnets and a pair of switches'having a switch arm forming the armature of the electromagnets, arranged to close the circuit with the solenoid when one of the-reaction devices is operated and a circuit connection operated by the magnets to disconnect the other reaction device from operating the solenoid.

9. In combination, a source of fluid pressure, a modulating valve controlling the delivery of increasing pressures to a device to perform work, and an electrical control mechanism, remote from the modulating valve and connected thereto by an electric circuit having a valve-operating solenoid therein, arranged to control the operation of the said valve, said control mechanism having manuallyv operable reaction device insaid solenoid and a reaction device producing a reaction corresponding to the pressures delivered, said solenoid having leverage connection to the valve providing a decreasing mechanical advantage upon energization of said solenoid and means for adjusting the eflective positions of the levers forming the connection to effect the decreasing mechanlcal advantage.

10. In a pressure modulating valve arrangement including electrical operating means for said modulating valve, controlled remotely, and simulating manual operation of said valve, said modulating valve communicating with a source of pressure and having means balancing the same against being affected in its operation by said pressure, said electrical means comprising a solenoid motor for moving said valve in the opening direction and connecting means between said solenoid and said valve including a cam driven by said solenoid and a lever effective to transmit force from said cam to-said valve, and means incluuding a manually operated rheostat for re-' motely adjusting the degree of energization 'of said solenoid in proportion to the pressure exerted on said manual means for effecting the opening of said modulating valve in proportion to said manual pressure.

11. In a pressure modulating valve arrangement including manually operated remote electrical control means therefor, a solenoid motor ,for operating said valve, under the influence of said control, means defining a lever and cam assembly connecting said solenoid with said modulating valve, said last named means comprising a first lever pivoted intermediate the ends thereof on a fixed pivot, one terminal portion .of said first lever being drivingly connected to said solenoid, one of said levers having a convex surface thereon, a second lever having a fixed pivot and engageable with said convex surface positions varying in distance from the pivot of said first lever depending upon the operative position of said solenoid and meansconnecting said second lever with said valve.

12. 'In a pressure modulating valve arrangement including remotely controllable electrical operating means for said valve effective to substantially simulate manual movement of said posed between said armature and said modulating valve effective to compensate for said variation in pull on said armature particularly that variation due to change in the relative position between said armature and said field, said means including a first lever formed with a convex cam 76 ioradjusting the degree of en ergization of said 11 iield in proportion to the manual pressure exerted on said last named means.

13. In a pressure modulating valve arrangement including remotely controllable electric means' for operating the same to approximately simulate manual operation, said arrangement including an on-modulating valve communicating with a source of pressure and having means balancing the same against being affected in its operation by said pressure, an oil-modulating or relief valve position adjacent said on-modulating valve, resilient means normally urging said relief or return valve to the open position, a

solenoid motor for first moving said relief valve into closed position and subsequently moving said modulating valve in the opening direction, the pulling force of said solenoid varying in'accordan ce with the operative position thereof, connecting means between said solenoid and said valves effective to compensate for said variation in the pulling force of said armature, said means including a first cam lever, a second follower lever for following said cam and effective to engage said cam at a varying distance from the axis of rotation of said cam in accordance with the position of said solenoid, a walking beam-like lever engaging both of said valves, and connecting means between said second lever and said walking beam intermediate said terminal portions of said walking beam whereby upon energization of said solenoid said relief valve is first closed and said modulating valve is subsequently moved in the direction of opening thereof, and means including manually operated rheostat for remotely adjusting the degree of energization of said solenoid in proportion to the manual pressure exerted thereon.

14. In a system for pressure utilization, an inlet for hydraulic fluid, a servo motor having a pressure responsive device receiving fluid therefrom, a pressure chamber means adapted to be connected to a pressure-responsive device to con- 12 trol the servo motor, said chamber having an inlet port and an outlet port, an inlet valve adapted to seat in said inlet port, having an area exposed to the pressure in said chamber in a direction tending to seat said inlet valve, an outlet valve adapted to seat in said outlet port and having an area exposed to pressure in said chamber in a direction tending to unseat said outlet valve, resilient means tending to seat said inlet valve, resilient means tending to unseat said outlet valve, means including a plunger exerting a varying pressure for operating the valves reactively to the pressures applied thereby and a resilient annular sealing washer of substantially rectangular cross section, around the inlet valve, the said seal comprising a spring means for providing a pre-- determined pinch so that the pressure from the pressure-exerting means acts on the inlet valve while minimizing the normaLfriction of the I seal so that the varying force acting on the plunger will be substantially the same when increasing amounts of pressure are applied as when decreasing amounts oi! pressure are applied.

, EDWARD A. ROCKWELL.

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